Siphon or eduction pipes are used on railway tank cars for loading and unloading through a valve on top of the car. The siphon or eduction pipe extends downward from the top unloading valve to the vicinity of the bottom of the tank.
It is desirable to locate the lower end of the eduction pipe as close as practically possible to the actual tank bottom. If the pipe terminates a given distance above the tank bottom, commodity will be left in the bottom of the car when it is unloaded, to the extent of the given distance.
As was discussed in application Ser. No. 827,129 filed Aug. 24, 1977, now U.S. Pat. No. 4,114,783, assigned to the same assignee as the present application, forces resulting from loading and unloading the lading, train action, and coupler impacts, cause the tank shell to flex in service. As a result the vertical diameter of the tank shell is not constant. Thus it is necessary to provide adequate clearance between the end of the eduction pipe and the bottom of the sump to accommodate this flexing.
The current state of the art is to provide a deep bowl sump in the tank bottom and extend the eduction pipe to a level approximately equal to the tank bottom. Recently enacted Association of American Railroads (AAR) and Department of Transportation (DOT) Regulations require that all fittings (such as sumps) extending more than one inch (1") below the shell envelope be provided with a suitable protective skid. This is an expensive and heavy device.
In application Ser. No. 827,129 a low profile sump and telescoping eduction pipe arrangement is disclosed including a lower fixed eduction pipe portion which extends into the lower portion of the sump, and an upper movable eduction pipe portion which telescopicly engages the lower eduction pipe portion for a distance at least equal to the distance that the tank top moves downwardly relative to the tank bottom when the car is impacted. Preferably the movable upper eduction pipe telescopes within the fixed, lower eduction pipe. This arrangement permits the use of a sump which fits within one inch of the shell envelope and therefore obviates the need for a protective skid. However, this arrangement requires the use of machined surfaces on the fixed and movable pipe portions and also requires sliding seals and wear rings. Formation of these machined surfaces and purchasing the seals and wear rings make this arrangement more expensive than desired.